In operation stop of a refrigerating apparatus, refrigerant accumulates into a compressor in some cases. For example, in the case where the compressor is accommodated in an outdoor unit installed outdoors, when the temperature of the compressor lowers in winter when the outdoor temperature is low, the refrigerant in a refrigerant circuit is condensed to accumulate in the compressor. The refrigerant accumulating in the compressor is mixed with lubricant oil stored in the compressor to lower the viscosity of the lubricant oil. When the compressor is activated in this state, the low-viscosity lubricant oil is supplied to the sliding portion of the compressor to cause lubrication failure, thereby inviting seizing. Further, the refrigerant mixed with the lubricant oil may be gasified at once at activation of the compressor to make the lubricant oil to be in a foamy state, causing insufficient oil supply.
To tackle this problem, a countermeasure has been provided which prevents accumulation of the refrigerant in the compressor by heating the compressor during operation stop of the refrigerating apparatus. For example, Patent Document 1 discloses that an electric heater is mounted at the compressor to heat the compressor through conduction of the electric heater. As well, Patent Document 2 discloses that low voltage at high frequency is applied to the coil of an electric motor provided at the compressor to cause the coil to generate Joule heat for heating the compressor without causing rotation of the electric motor.
In the case where the compressor is heated during the operation stop of the refrigerating apparatus as above, energy, such as electric power and the like is consumed even during the operation stop of the refrigerating apparatus. In order to solve this problem, Patent Document 1 discloses that: whether to conduct the electric heater is judged on the basis of the outdoor air temperature and the indoor air temperature; and when it is judged that compressor heating is unnecessary, the conduction of the electric heater is stopped. Specifically, in Patent Document 1, when the difference between the outdoor air temperature and the indoor air temperature is equal to or larger than a predetermined value and the outdoor air temperature is equal to or higher than a predetermined value, the conduction of the electric heater is stopped on the ground that it is judged that less mount of the refrigerant will accumulate into the compressor.
Patent Document 1: Japanese Patent Application Laid Open Publication No. 2002-106981
Patent Document 2: Japanese Patent Application Laid Open Publication No. 2002-031386